Method for producing ceramic brake disks from bmc

ABSTRACT

The invention relates to a method for producing ceramic brake discs, comprising the following steps: a) producing a BMC compound ( 2 ) with a matrix consisting of phenol resin and with carbon reinforcement fibres, the length of the carbon fibres being between 6 mm and 50 mm; b) poducing a green compact of the ceramic brake discs from the BMC compound (2) in a transfer moulding or injection compression moulding process, c) pyrolysing the green compact in order to produce a porous moulded body, and d) melt-infiltrating the porous moulded body with a melt preferably a silicon melt, in order to produce a moulded body with reaction-bonded fibres.

[0001] The invention relates to a process for producing ceramic brakedisks.

[0002] The use of carbon-fibre-reinforced carbon (CFC materials) inbrake disks is limited to about 500° C. on account of the oxidationsensitivity of the carbon fibres. One application is, for example, inFormula One vehicles. An exact matching of the CFC disk quality isnecessary, corresponding to the prevailing weather conditions. Theservice life only extends over one race. The material is not suitablefor use in production vehicles. Disadvantages are the high cost, thehigh degree of wear, and the weather-dependent and temperature-dependentcoefficient of friction.

[0003] With short-carbon-fibre-reinforced ceramic bodies (ceramic matrixcomposites (CMC)) it is possible for higher strength to be obtained athigh temperatures. Frequently, however, no adequate damage tolerance forhigh-performance applications is obtained such as is demanded for brakedisks, for example. The production of such a material with short-fibrereinforcement is undertaken by the so-called structural-granulationmethod, as described in DE 197 11 829 C1.

[0004] With a view to enhancing the damage tolerance, it is state of theart to introduce a long-fibre reinforcement with carbon-fibre fabric.This process is very elaborate and cost-intensive with regard to thepreparation of blanks, the amount of blanking waste and the cost of thecarbon-fibre semifinished product.

[0005] The production of brake disks from ceramic advanced SMC (sheetmoulding compound) with short-fibre and long-fibre reinforcementaccording to PCT/EP00/00253 and DE 199 01 215 A1 is a more economicalalternative, with higher damage tolerance than the reinforcement withcarbon-fibre fabric. However, the preparation of blanks for the pressingof the brake disks is still too cost-intensive, on account of the effortinvolved.

[0006] For the large-scale production of brake disks, a modern andrational process technology is required that is directed towards thefuture.

[0007] Therefore a process is proposed for the production of ceramicbrake disks from BMC (bulk moulding compound), comprising the followingprocess steps:

[0008] a) production of a BMC compound (2) with a matrix consisting ofphenolic resin and with reinforcing fibres consisting of carbon, thelength of the carbon fibres being between 6 mm and 50 mm,

[0009] b) production of a green compact of the ceramic brake disks fromthe BMC compound (2) using the transfer-moulding process orinjection/compression process,

[0010] c) pyrolysing the green compact for the purpose of producing aporous moulded article and

[0011] d) melt infiltration of the porous moulded article with a melt,preferably with a silicon melt, for the purpose of producing a mouldedarticle with reaction-bonded fibres.

[0012] BMC moulding compounds and their composition are described, forexample, in Kunststoff-Handbuch, Wilbrand Woebcken, Edition 10,Duroplaste, Hanser Verlag, 1988, pp 312-323.

[0013] Features of the present invention:

[0014] Production of a BMC with ceramic matrix and carbon-fibrereinforcement.

[0015] Trouble-free manufacture of relatively large batch quantities. Incomparison with the SMC production process, EMC can be manufacturedrationally using CMC (continuous-moulding-compound) process technologyin the semifinished-product form that is suitable for theinjection-moulding process or transfer-moulding process. These processtechnologies are more rational, less cost-intensive and lessmanpower-intensive than the processing of SMC in the pressing process.Larger batch, quantities can be manufactured without difficulty.

[0016] Generation of the requisite fibrous structure for the brake diskin the course of processing of the compound to form brake disks.

[0017] According to the invention, BMC with a matrix consisting ofphenolic resin and a carbon-fibre reinforcement is used as compound. Thelength of the reinforcing fibres may be between 6 mm and 50 mm. With aview to optimising the ceramic properties, working may take place withseveral different lengths of fibre in one compound

[0018] Production of the BMC is undertaken in a facility operatingcontinuously (continuous impregnated compound). The compound that isproduced using this process technology has only a slight deteriorationof the carbon fibre and is therefore preferred. However, manufacture ofthe ceramic BMC is also possible in the kneaders that are conventionalfor BMC production.

[0019] Processing of the ceramic advanced BMC according to the inventionis undertaken using the transfer-moulding process orinjection/compression process. The advantages of this process technologyconsist in the more rational processing with less manual effort than inthe pressing process with SMC, with the elaborate creation of blanks.With a view to adapting the properties of the material to theapplication for brake disks, the fibrous structure can be generated whenthe compound is introduced into the moulding tool. By virtue of the useof multi-component injection-moulding technology, several compounds withdifferent lengths of fibre can be introduced into the toolsimultaneously, and corresponding fibrous structures can be generated.

[0020] The transfer-moulding process may preferably be employed. Thetransfer-moulding process is the combination of the pressing techniquewith an injection cylinder in the middle of the tool. Via a centralcylinder and piston, in which the requisite quantity of compound hasbeen introduced, the moulding compound is injected into the closed orslightly open tool. The cylinder may also be filled with the aid of aninjection-moulding machine or an extruder.

[0021] The injection/compression process is a further possibility forproducing the brake disks according to the invention, or, to be moreexact, the green compact for them. The ceramic advanced BMC is injectedinto the closed or slightly open tool using an injection-mouldingmachine that has been adapted to the ceramic matrix in its pressure andtemperature settings. After the quantity of compound has been introducedinto the heated tool, the tool is closed and the compound is distributedin the mould.

[0022] In an advantageous refinement of the invention, the mouldedarticles produced by the process according to the invention, or, to bemore exact, the brake disks, exhibit ventilation fins on the insidediameter on both sides of the ceramic brake disk. The cooling by ambientair is improved by this means.

[0023] In addition, on both sides of the ceramic brake disk, on thesurface thereof, uninterrupted ventilation ducts are disposed inadvantageous manner in straight, circular or involute arrangement forthe purpose of dissipating heat.

[0024] The cross-section of the ventilation ducts expediently has anangular or round form, with widths amounting to between 1 mm and 10 mm.

[0025] The present invention describes, in detail:

[0026] BMC with ceramic matrix and carbon-fibre reinforcement forceramic brake disks.

[0027] Reinforcing-fibre lengths from 6 mm to 50 mm.

[0028] One or more lengths of fibre in one compound.

[0029] Fibre proportions from 10 vol. % to 60 vol. %.

[0030] Extrusion of the BMC into cylindrically shaped portions orextrusion into plastic bags with a view to simple charging intoinjection-moulding machines.

[0031] Processing of the ceramic BMC in injection-moulding machinesusing the injection/compression process or in suitable presses using thetransfer-moulding process.

[0032] Generation of the fibre arrangement by source flow of the ceramicBMC when the moulding compound is introduced into the brake-disk tool orinto the press.

[0033] Generation of fibre orientations in the peripheral direction ofthe ceramic brake disk.

[0034] By varying the tool opening when the ceramic BMC is introduced,an influence can be exerted on the fibre orientation in the peripheraldirection. Interlocking and alignment in the second and third dimensionstake place when the tool is closed.

[0035] Disk design with ventilation fins on the inside diameter on bothsides of the ceramic brake disk.

[0036] Uninterrupted ventilation ducts in straight, circular or involutearrangement on both sides of the ceramic brake disk for the purpose ofdissipating heat on the surface of the brake disk.

[0037] Cross-section of the ventilation ducts in angular or round form,and widths from 1 mm to 10 mm.

[0038] Further features of the invention arise out of the Figures whichare described below. Shown are:

[0039]FIGS. 1a-1 c the injection/compression moulding of the greencompact of ceramic brake disks,

[0040]FIGS. 2a-2 d the transfer moulding of the green compact of ceramicbrake disks,

[0041]FIG. 3 the fibre orientation as a result of central injecting,

[0042]FIG. 4 a ceramic brake disk with a special fin design, and

[0043]FIGS. 5 and 6 in each case, a ceramic brake disk with specialventilation ducts.

[0044]FIGS. 1a to 1 c show the injection/compression moulding of thegreen compact of ceramic brake disks in an injection-moulding machinewhich consists of an upper part 9 and a lower part 10. Via a nozzle 11arranged centrally in the upper part 9—in the case shown, with twoinjection ducts 12—the requisite quantity of BMC compound 2 is injectedinto the closed or slightly open tool 6. Subsequently the tool 6 isclosed, i.e. the upper part 9 is displaced in the direction of the lowerpart 10, and in the process the compound 2 is pressed orcompression-moulded into the desired shape. The lower part 10 and theupper part 11 have a shape that corresponds to the design of the desiredceramic brake disk.

[0045]FIG. 1a shows the tool 6 in the open state prior to injection ofthe compound. FIG. 1b shows the tool 6 in the slightly open state, i.e.the upper part 9 is raised slightly away from the lower part 10. In thisstate the compound 2 is injected via the nozzle 11 with the injectionducts 12. The temperature of the tool 6 and the pressure are adapted tothe requirements of the compound 2.

[0046]FIG. 1c shows the actual pressing or compression moulding, i.e.the upper part 9 is moved in the direction of the lower part 10, and inthis way the green compact is pressed or compression-moulded.Subsequently the tool 6 is opened, the green compact is taken out andsupplied to stages for further treatment such as pyrolysation and meltinfiltration.

[0047]FIGS. 2a to 2 d show the transfer moulding of the green compactfor ceramic brake disks.

[0048]FIG. 2a shows the tool 4 in the wide-open state, i.e. the upperpart 9 is raised far away from the lower part 10. In the middle of thetool 4, i.e. of the lower part 10, an injection cylinder 3 is arrangedwhich contains a displaceable piston 5.

[0049]FIG. 2b shows the tool 4 in the partly closed state, the requisitequantity of compound 2 being disposed in the injection cylinder 3 on thepiston 5. This quantity is fed in, or even injected, by conventionalmeans. In this Figure the piston 5 is shown in the retracted state.

[0050]FIG. 2c shows the tool 4 shortly prior to completed processing ofthe green compact. The piston 5 is located in the almost extendedposition, and the compound 2 already almost fills out the entire mould.

[0051]FIG. 2d shows the tool 4 after the transfer-moulding operation.The tool 4 is now completely closed, and the piston 5 is located in itsfinal position. The green compact has been moulded and can be taken outafter the tool 4 has been opened.

[0052]FIG. 3 shows the fibre orientation 15 in a section through a greencompact 13. A preorientation of the fibres is effected as a result ofthe central injecting via the nozzle 14. When the tool is closed, asdescribed above, a further orientation of the reinforcing fibressubsequently takes place in the radial direction.

[0053]FIG. 4 shows a finished ceramic brake disk 1 with a two-sided findesign for the purpose of cooling the surface of the disk. To this end,ventilation fins 7 are arranged on the inside diameter. In this specialcase the ventilation fins 7 extend in the radial direction. Theventilation fins 7 are uniformly distributed in the peripheraldirection.

[0054]FIGS. 5 and 6 show ventilation ducts 8 on both sides of theceramic brake disk 1. In FIG. 5 these ventilation ducts extend to thesurface of the brake disk in radial manner, and in FIG. 6 in involutemanner. These ventilation ducts 8 have been directly created by virtueof slit-shaped indentations in the course of transfer moulding orinjection/compression moulding of the green compact.

1. A process for producing ceramic brake disks (1) from BMC, comprisingthe following process steps: a) production of a BMC compound (2) with amatrix consisting of phenolic resin and with reinforcing fibresconsisting of carbon, the length of the carbon fibres being between 6 mmand 50 mm, b) production of a green compact of the ceramic brake disksfrom the BMC compound (2) using the transfer-moulding process orinjection/compression process, c) pyrolysing the green compact for thepurpose of producing a porous moulded article and d) melt infiltrationof the porous moulded article with a melt, preferably with a siliconmelt, for the purpose of producing a moulded article withreaction-bonded fibres.
 2. Process according to claim 1, characterisedin that different lengths of fibre are found in the BMC compound (2). 3.Process according to claim 1 or 2, characterised in that the proportionof fibre in the compound (2) amounts to between 10 per cent by volumeand 60 per cent by volume.
 4. Process according to one of claims 1 to 3,characterised in that several compounds (2) with varying lengths offibre are introduced simultaneously into the transfer-moulding tool orinjection/compression-moulding tool.
 5. Process according to one ofclaims 1 to 4, characterised in that in the case of thetransfer-moulding process there is arranged in the middle of the tool(4) an injection cylinder (3) in which the requisite quantity ofcompound (2) is introduced and injected into the open tool (4) byreciprocating motion of the piston (5) in the injection cylinder (3). 6.Process according to one of claims 1 to 4, characterized in that theinjection/compression-moulding process is undertaken in aninjection-moulding machine which has been adapted to the BMC compound(2) in its pressure and temperature settings, and the compound (2) isinjected into the closed or slightly open tool (6) and subsequently thetool (6) is closed and in the process the compound (2) is pressed orcompression-moulded into the desired shape.
 7. Process according to oneof claims 1 to 6, characterised in that the ceramic brake disks (1)exhibit ventilation fins (7) on the inside diameter on both sides of theceramic brake disk (1).
 8. Process according to one of claims 1 to 7,characterised in that uninterrupted ventilation ducts (8) in straight,circular or involute arrangement are disposed on both sides of theceramic brake disk (1) on the surface of the brake disk for the purposeof dissipating heat.
 9. Process according to claim 8, characterised inthat the cross-section of the ventilation ducts (8) is in angular orround form, and widths amount to between 1 mm and 10 mm.